1. Field of the Invention
The present invention relates generally to methods of reducing thrombogenicity associated with polymer resin articles. More particularly, the present invention relates to a method for producing a heparin coated polymeric article wherein the polymeric article is treated with a plasma prior to attachment of the heparin.
2. Description of Prior Art
U.S. Pat. No. 3,846,353, to Grotta indicates that polymers, both natural and synthetic and particularly certain synthetic plastics have come to the fore as preferred materials for prosthetic devices. Their major drawback, however, is their thrombogenicity. Even though plastics are used in various apparatus such as heart-lung machines, kidney machines, and artificial heart valves and patches, the tendency of these materials to cause coagulation necessitates the use of anticoagulants such as heparin. Even such plastics as Teflon (polytetrafluorethylene) and the silicone rubbers which are more compatible with blood than most plastics, still show thrombogenic characteristics. The first real advance in the preparation of nonthrombogenic materials was described by Dr. Vincent Gott. The method used by Dr. Gott comprised treating a graphited surface first with Zephiran (benzalkonium chloride) and then with heparin. Materials treated in this way were nonthrombogenic in vivo for long periods of time. The major disadvantage, however, with these materials, was that the method could only be practiced on rigid plastics and a need still exists for a suitable flexible nonthrombogenic plastic, as well as a method of producing the same.
Various methods have been devised for introducing antithrombogenicity which involve chemically bonding a quaternary ammonium salt to the polymeric surface and then heparinizing the thus modified surface. Illustrative of these methods are the procedures described in U.S. Pat. No. 3,634,123 to Eriksson wherein an article having a plastic surface is heated to near or above its softening point in an aqueous solution of a cationic surface active agent, as, for example, long chain alkylamine hydrohalides. In such manner, the surface active agent permeates and thereby becomes affixed to the resin surface. In addition, the hydrocarbon portion of the surface-active agent is thought to become bound to the surface of the plastic. Subsequent digestion of the plastic articles with an aqueous solution of heparin provides articles of enhanced antithrombogenicity.
A further improvement is described in by U.S. Pat. No. 3,810,781 to Eriksson, wherein heparinized plastic surfaces are stabilized by cross linking the bonded heparin molecules with dialdehydes. By this procedure, while some improvement in stability results, not all of the bonded heparin is impervious to desorption by washing.
The binding of substantially greater quantities of heparin to the polymer surface is described in U.S. Pat. No. 4,349,467 to Dudley, wherein the step of heparinization is carried out with aqueous solutions of heparin of 5% or greater concentration. Using this procedure, up to 18 ug/cm of heparin are bound to a polyurethane surface through the surface active agent.
Many of the drawbacks and disadvantages of earlier methods for rendering polymeric surfaces non-thrombogenic are eliminated by the teaching of the above named patents. There remains, however, a need for methods to adhere higher quantities of heparin, impervious to desorption, to polymeric surfaces for use in articles which will be in contact with blood for prolonged periods of time. These needs are met by the method of the current invention incorporating a plasma treatment of the resin surface before the heparinization step.
The process of formation of a plasma by electromagnetic activation of a gas by either a glow discharge or a corona discharge, and the use of such plasma for activating polymeric surfaces is known to accomplish various purposes. For example, U.S. Pat. No. 3,663,265 to Lee teaches deposition of vaporized polymeric material onto substrate surfaces by treatment of the polymeric material with a plasma from an inert gas whereby the polymer is vaporized and contacted with the substrate to form the coating. In U.S. Pat. No. 4,091,166 to Kubacki, a plastic surface is treated with a plasma of boron trifluoride, optionally admixed with an organic monomer to deposit a boron trifluoride containing coating. U.S. Pat. No. 3,415,683 to Coffman discloses formation of deposits from organic materials on substrates such as bare metals in a corona reaction. U.S. Pat. No. 3,518,108 to Heiss teaches formation of polymer coatings from aromatics, aliphatics and silicones in a plasma of inert gas or hydrogen.
U.S. Pat. No. 3,776,762 to Bernath teaches glow discharge deposition of fluorocarbon polymeric coatings onto metallic or non-metallic surfaces by passing DC current through a low pressure atmosphere of the monomer. U.S. Pat. No. 4,326,532 to Hammar discloses the use of a plasma for priming the surface of a polymeric resin for deposition of a coating of chitosan receptive to subsequent heparin binding.